Tommy
Administrator
Member since January 2013
Posts: 12,717
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Post by Tommy on Nov 10, 2017 11:39:08 GMT -5
I crush the matrix, I don'r grind it. It crushes down to a fine sand. I make a dam out of masking tape and form it around the cab, fill it in with the mix & then grind the back flat after it hardens. I'm just learning all kinds of stuff from you this week sir. May I ask how you accomplish crushing it?
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Post by pauls on Nov 10, 2017 15:07:33 GMT -5
A woman at my club was backing opals with car radiator putty it seemed to work, It came in a small tube too so handy to use.
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monna0000
starting to spend too much on rocks
Member since May 2016
Posts: 243
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Post by monna0000 on Nov 10, 2017 16:33:18 GMT -5
I'm a bit embarrassed to say since i dont know if it's a big NO NO but i have just used an old CD and epoxy glue the few times I've needed to back a cab.
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Post by Psycho on Nov 10, 2017 16:50:49 GMT -5
Well CDs are resin and plastic, would be a good use for all the scratched ones the kids destroyed I guess lol. Any opinions?
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zarguy
fully equipped rock polisher
Cedar City, Utah - rockhound heaven!
Member since December 2005
Posts: 1,791
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Post by zarguy on Nov 10, 2017 18:39:48 GMT -5
I crush the matrix, I don'r grind it. It crushes down to a fine sand. I make a dam out of masking tape and form it around the cab, fill it in with the mix & then grind the back flat after it hardens. I'm just learning all kinds of stuff from you this week sir. May I ask how you accomplish crushing it? I tried a hammer, but chunks were flying all over the garage. I had more success with a Harbor Freight arbor press. A machinist friend made a tube, cap & ram that you hit with a hammer, but I think the press works best. I'm still experimenting. Lynn
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Tommy
Administrator
Member since January 2013
Posts: 12,717
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Post by Tommy on Nov 10, 2017 18:47:18 GMT -5
I'm a bit embarrassed to say since i dont know if it's a big NO NO but i have just used an old CD and epoxy glue the few times I've needed to back a cab. Whatever works I would say. I don't think there are any "rules" about it. Some of our more 'experienced' cabbers who were doing it while I was still wet behind the ears might disagree with me One of the first things I tried was thin gloss polycarbonate. Our die cutting operation at work produced an endless supply of polycarb scraps going in the garbage every day so I was excited to try it but I remember it failing miserably - either breaking or melting I can't remember..
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Post by gmitch067 on Nov 10, 2017 23:26:39 GMT -5
I'm a bit embarrassed to say since i dont know if it's a big NO NO but i have just used an old CD and epoxy glue the few times I've needed to back a cab. An old CD would work!!! Ahhh.... How the rocks would sing! YES! Also, if the cab was semitransparent to transparent stone, the CD would allow good reflection from the backing - giving a little 3D effect. I am sure that some of the purist members are probably having heart attacks about now, but sometimes you just got to have FUN!
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Post by Rockoonz on Nov 11, 2017 0:52:17 GMT -5
Elizabeth has backed montana moss with mirror glass, very cool effect. I have backed all my triplets and intarsia with black basinite and argillite so far with good results. Have a piece of Spencer opal backed in red glass that I bought that way, haven't capped it yet but I think it will end up pretty cool if I don't mess it up. The thing my excellent mentor taught me about backing or capping with clear is to do everything to avoid bubbles. Mix epoxy without lifting the stir stick from the mixing surface and wave a butane flame over the epoxy to pull the bubbles out then assemble like closing the cover on a book. With the 330 epoxy mixing with a little more hardener than resin is better than the opposite, save a couple that are still sticky 5 years later.
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Post by parfive on Nov 11, 2017 2:25:08 GMT -5
Never had a problem using Krazy Glue on a doublet.
Nice and thin, unlike epoxy, and no bubbles.
Alt-basanite > black onyx, aka dyed Brazilian agate.
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Post by Peruano on Nov 11, 2017 6:55:00 GMT -5
If you use a cd, place the glue on the playing side, not the label side. The label can float off in mineral oil, and hence would release from the stone. Maybe someone mentioned it and I missed it, but for many years the standard was to use vinyl records. 33 and a third work but I'm sure the technique was developed on 78's. The grooves help with glue adhesion.
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Post by Bluesky78987 on Nov 11, 2017 10:21:20 GMT -5
I used a CD to back a composite cab I made (it was an opaque stone though). I tried using a record for that one, a 33, but the record was too thick, and grinding plastic down to your preferred thickness doesn't work very well. The CDs start out around the right thickness.
I used a regular (back surface) mirror for my recent woodward ranch cab triplet experiment and it was ok, but the glass was uncooperative to cut (I didn't have a glass scorer back then). Folks use a front surface mirror regularly I think also, and I got a couple small ones from ebay but haven't mounted them yet.
One "principle" to note: the "smear goup, or goup mixed with rock grindings" on the back of a stone method is great for stones that aren't flat on the back, like turquoise.
It might also be great for a stone you think might just crack, I don't know, maybe somebody else can say.
This is a fantastic thread!
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RWA3006
Cave Dweller
Member since March 2009
Posts: 4,254
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Post by RWA3006 on Nov 11, 2017 10:43:22 GMT -5
Good thread guys. Wondering ... has anyone tried using ceramic glass for backing? Not the same as tempered glass. When I was in the fireplace industry many of the higher quality wood burning stoves and fireplaces used ceramic glass (still do). The advantage of ceramic glass is it is very tough and takes thermal abuse well. The disadvantage is it was not easy to cut using traditional glass cutting equipment. Seems like I remember something about it needing a laser to cut it. I do think it would grind and polish ok with conventional lapidary equipment though. Thoughts?
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